It is a common practice to color silver halide emulsion layers and other hydrophilic colloid layers in a silver halide photographic material in order to effect absorption of light of specific wavelengths.
The normal practice when it is necessary to control the spectral composition of light that is incident on a photographic emulsion layer is to provide a colored layer on the side that is farther from the support than the photographic emulsion layer. Such a colored layer is called a filter layer. If there is a plurality of photographic emulsion layers, filter layers may be provided between the emulsion layers.
Halation, or blurring of images, occurs due to light that has been scattered during or after passage through a photographic emulsion layer being reflected at the interface of the emulsion layer and the support or at the surface of photosensitive material on the opposite side to the emulsion layer. To prevent such halation it is known to provide a colored layer called an antihalation layer between the photographic emulsion layer and the support or on the side of the support that is opposite to the photographic emulsion layer. If there is a plurality of photographic emulsion layers, the antihalation layers may be provided between the emulsion layers.
It is also known to color a photographic emulsion layer in order to prevent a reduction of image sharpness due to scattering of light inside the layer (a phenomenon which is generally called "irradiation").
Normally, dyes are included in these hydrophilic colloid layers that are to be colored. The dyes used in this case must meet the following conditions.
(1) They must display suitable spectral absorption in correspondence to the purpose of their use.
(2) They must be inert in terms of photographic chemistry. That is, they must have no adverse effects on the performance of silver halide emulsion layers in the chemical sense, e.g., effects such as lowering of the speed, fading of latent images or fogging.
(3) Either they must be decolored or they must be eluted in processing solutions or washing water during the course of photographic processing, so that they are not responsible for harmful coloration remaining in the photographic material after processing.
(4) They must not diffuse from a dyed layer to other layers.
(5) They must have excellent stability and not be subject to discoloration or fading with the pussage of time in bath solutions or the photographic material.
In particular, in most cases where colored layers are filter layers or where they are antihalation layers provided on the same side of a support as the photographic emulsion layers, it is necessary that the layers concerned be selectively colored and there be essentially no extension of coloration to other layers. Otherwise harmful spectral effects are exerted on the other layers and the effects of the filter layer or antihalation layer may be cancelled out. However, frequently when a layer to which a dye has been added and another hydrophilic colloid layer are in contact while in a wet state, a portion of the dye diffuses from the former to the latter layer. Much past effort has been directed to preventing such diffusion of dyes.
For example, methods in which dissociated anionic dyes are introduced into layers together with hydrophilic polymers which carry an opposite charge and serve as mordants so as to localize the dyes in specific layers through interactions with dye molecules are disclosed in, e.g., U.S. Pat. Nos. 2,548,564, 4,124,386 and 3,625,694.
Further, methods for dyeing specific layers by using water-insoluble dye solids are disclosed in, e.g., JP-A-56-12639, JP-A-55-155350, JP-A-55-155351, JP-A-63-27838, JP-A-63-197943 (the term "JP-A" as used herein means an "unexamined Japanese patent application") and European Patent 15601.
Also, methods for dyeing specific layers by using metal salt micrograins on which dyes are adsorbed are disclosed in, e.g., U.S. Pat. Nos. 2,719,088, 2,496,841 and 2,496,843 and JP-A-60-45237.
However, even when these improved methods are used, there is the problem that the rate of decoloration in development processing is slow. Then, when certain conditions are altered, e.g., speeding-up of processing, improvement of processing solution compositions or improvement of photographic emulsion compositions, it is not always possible to guarantee proper performance of the decoloration functions.
There is also a demand for hydrophilic colloid layers which absorb light of, e.g., the 700 to 1000 nm region, and so can be used in a photographic material that is sensitive to near-infrared light and which contains dyes that are in the form of solid micrograin dispersions and are decolored or elute satisfactorily during development processing. But dyes suitable for this application have not been found.